Method and system for recognizing radio link failures associated with HSUPA and HSDPA channels

ABSTRACT

A method and system for detecting radio link (RL) failures between a wireless transmit/receive unit (WTRU) and a Node-B are disclosed. When signaling radio bearers (SRBs) are supported by high speed uplink packet access (HSUPA), an RL failure is recognized based on detection of improper operation of at least one of an absolute grant channel (AGCH), a relative grant channel (RGCH), a hybrid-automatic repeat request (H-ARQ) information channel (HICH), an enhanced uplink dedicated physical control channel (E-DPCCH) and an enhanced uplink dedicated physical data channel (E-DPDCH). When SRBs are supported by high speed downlink packet access (HSDPA), an RL failure is recognized based on detection of improper operation of at least one of a high speed shared control channel (HS-SCCH), a high speed physical downlink shared channel (HS-PDSCH) and a high speed dedicated physical control channel (HS-DPCCH).

CROSS REFERENCE TO RELATED APPLICATION

This application is continuation of U.S. patent application Ser. No.12/723,211 filed Mar. 12, 2010 which is a continuation of U.S. patentapplication Ser. No. 11/322,704 filed Dec. 30, 2005 which claims thebenefit of U.S. Provisional Application No. 60/651,594 filed Feb. 9,2005 which is incorporated by reference.

FIELD OF INVENTION

The present invention is related to a wireless communication systemincluding a wireless transmit/receive unit (WTRU) and a Node-B. Moreparticularly, the present invention is related to a method and systemfor recognizing radio link (RL) failures associated with high speeduplink packet access (HSUPA) and high speed downlink packet access(HSDPA) channels established between the WTRU and the Node-B.

BACKGROUND

In a third generation partnership project (3GPP) wireless communicationsystem, signaling radio bearers (SRBs) are used to maintain aconnection, (i.e., an RL), between a WTRU and a Universal TerrestrialRadio Access Network (UTRAN). When reception of the physical channelconnecting the WTRU and Node-B is below a quality threshold or can notbe detected, (i.e., the physical channel that allows for signalinginformation to be exchanged between the WTRU and UTRAN has failed), anRL failure is declared, and the WTRU and the UTRAN initiate proceduresto reestablish the connection between the WTRU and the UTRAN.

In order to realize the loss of the SRBs and take a proper action, theWTRU and the UTRAN constantly monitor for an occurrence of an RLfailure. A primary objective of the RL failure detection procedure is todetect failure of the transport channels (TrCHs) and physical channelsto which the SRBs are mapped.

In the 3GPP wireless communication system, SRBs are mapped to dedicatedtransport channels (DCHs) which are in turn mapped to dedicated physicalchannels (DPCHs). A DPCH comprises a dedicated physical control channel(DPCCH) and a dedicated physical data channel (DPDCH).

The criteria to detect the status of the DPCHs and DCHs includesestimation of the DPCCH quality, (and comparison to a predeterminedthreshold), and/or collection of statistics of correct reception of datapackets on a DPCH based on cyclic redundancy check (CRC). When thecriteria are met, the WTRU and the UTRAN invoke a procedure to releaseand reestablish the connection between the WTRU and the UTRAN.

In the 3GPP wireless communication system, both continuous services,(e.g., speech), and interactive services, (e.g., web browsing), aresupported. Dedicated channels are efficient for supporting continuousservices, while shared channels are efficient for supporting interactiveservices. The shared channels provide more efficient use of radioresources and improved quality of service (QoS) for interactiveservices. However, when the service is mapped to shared channels, theuse of dedicated channels for SRBs is inefficient since the trafficrequirement is not continuous.

In 3GPP wireless communication systems, HSUPA and HSDPA primarilyutilize high speed shared channels for services that do not requirecontinuous channel allocations. These channels utilize fast physical andmedium access control (MAC) layer signaling between the WTRU and theNode-B for channel assignment and hybrid-automatic repeat request(H-ARQ) for efficient and fast recovery of failed transmissions.

If the SRBs are supported by either HSUPA or HSDPA channels rather thandedicated channels, it is possible that SRBs may fail, even thoughdedicated channels are still operating. Furthermore, the criteria todetect the dedicated channel failure may not be met even though theHSUPA or HSDPA channels supporting the SRBs are not operating. In thiscase, RL failure will not be detected even though the SRBs have alreadylost connectivity.

SUMMARY

The present invention is related to a method and system for detecting RLfailures between a WTRU and a Node-B when SRBs are supported by HSUPA orHSDPA. When SRBs are supported by the HSUPA, the WTRU monitors at leastone of an absolute grant channel (AGCH), a relative grant channel (RGCH)and an H-ARQ information channel (HICH) and recognizes an RL failurebased on detection of improper operation of at least one of the AGCH,the RGCH and the HICH. The Node-B monitors at least one of an enhanceduplink dedicated physical control channel (E-DPCCH) and an enhanceduplink dedicated physical data channel (E-DPDCH) and recognizes the RLfailure based on detection of improper operation of at least one of theE-DPDCH and the E-DPCCH.

When SRBs are supported by the HSDPA, the WTRU monitors at least one ofa high speed shared control channel (HS-SCCH) and a high speed physicaldownlink shared channel (HS-PDSCH) and recognizes an RL failure based ondetection of improper operation of at least one of the HS-SCCH and theHS-PDSCH. The Node-B monitors a high speed dedicated physical controlchannel (HS-DPCCH) and recognizes an RL failure based on detection ofimproper operation of the HS-DPCCH.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description, given by way of example and to be understood inconjunction with the accompanying drawings wherein:

FIG. 1 is a wireless communication system including a WTRU and a Node-Bwhich communicate via HSUPA channels established in accordance with thepresent invention;

FIG. 2 is a block diagram of an exemplary WTRU used in the system ofFIG. 1;

FIG. 3 is a block diagram of an exemplary Node-B used in the system ofFIG. 1;

FIG. 4 is a scheme for recognizing an RL failure at the WTRU utilizingthe HSUPA channels of the system of FIG. 1;

FIG. 5 is a scheme for recognizing an RL failure at the Node-B utilizingthe HSUPA channels of the system of FIG. 1;

FIG. 6 shows HSDPA channels established between the WTRU and the Node-Bof the system of FIG. 1;

FIG. 7 is a scheme for recognizing an RL failure at the WTRU utilizingthe HSDPA channels of FIG. 6; and

FIG. 8 is a scheme for recognizing an RL failure at the Node-B utilizingthe HSDPA channels of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “WTRU” includes but is not limited to a userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, or any other type of device capable of operating in a wirelessenvironment. When referred to hereafter, the terminology “Node-B”includes but is not limited to a base station, a site controller, anaccess point or any other type of interfacing device in a wirelessenvironment.

The features of the present invention may be incorporated into anintegrated circuit (IC) or be configured in a circuit comprising amultitude of interconnecting components.

FIG. 1 is a diagram of a wireless communication system 100 including aWTRU 102 and a Node-B 104 which communicate via HSUPA channelsestablished between the WTRU 102 and the Node-B 104 in accordance withthe present invention. Between the WTRU 102 and the Node-B 104, anE-DPDCH 106, an AGCH 108, an RGCH 110 (optional), an HICH 112 and anE-DPCCH 114 are established.

FIG. 2 is a block diagram of an exemplary WTRU 102 used in the system100 of FIG. 1. The WTRU 102 includes a transceiver 202, a controller 204and a measurement unit 206.

FIG. 3 is a block diagram of an exemplary Node-B 104 used in the system100 of FIG. 1. The Node-B 104 includes a transceiver 302, a controller304, a measurement unit 306, a scheduler 308 and an H-ARQ processingunit 310.

In accordance with one embodiment of the present invention, thetransceiver 202 of the WTRU 102 sends a rate request with schedulinginformation to the Node-B 104 via the E-DPCCH 114 and the E-DPDCH 106.The transceiver 302 of the Node-B 104 receives the rate request and thescheduler 308 analyses the rate request and generates and sendsscheduling an assignment to the WTRU 102 via the AGCH 108, (oroptionally via the RGCH 110), to control the uplink access and maximumrate that the WTRU 102 is allowed to transmit. The transceiver 202 ofthe WTRU 102 sends uplink (UL) data to the Node-B 104 via the E-DPCCH114 and the E-DPDCH 106. When the transceiver 302 of the Node-B 104receives the UL data, the H-ARQ processing unit 310 of the Node-B 104generates H-ARQ feedback to the WTRU 102 via the HIGH 112. Thecontroller 204 of the WTRU 102 and the controller 304 of the Node-B 104detect the RL failure in accordance with the present invention, whichwill be explained in detail hereinafter.

Referring to FIG. 1, certain radio bearers (RBs) may be assigned aguaranteed bit rate that does not require a rate request and Node-Bscheduling. When configured for a guaranteed bit rate, the rate requeston the E-DPCCH 114 and/or the E-DPDCH 106, and the scheduling granttransmitted on the AGCH 108 and/or the RGCH 110, is not required fortransmission of UL data.

Still referring to FIG. 1, when allowed to transmit in the uplink,either by reception of a scheduling grant or by a configured guaranteedbit rate, the WTRU 102 utilizes H-ARQ procedures for transmission. Theremay be several H-ARQ processes operating independently between the WTRU102 and the Node-B 104. In the WTRU 102, each H-ARQ process transmits ablock of data via the E-DPDCH 106 and waits for H-ARQ feedback on theHICH 112, (i.e., a positive acknowledgement (ACK) or a negativeacknowledgement (NACK)), from the Node-B 104.

In the Node-B 104, if the CRC check on the received data block issuccessful, an ACK is transmitted. Otherwise, a NACK may optionally betransmitted via the HICH 112 for each H-ARQ transmission. If a NACK isreceived by the WTRU 102, a previous data block is retransmitted as longas the maximum number of retransmissions is not exceeded. If an ACK isreceived or the maximum number of retransmission is exceeded, the WTRUH-ARQ process may be assigned a new transmission. The rate requests andscheduling assignments may coincide with uplink data transmissions, andseveral independent H-ARQ transmissions and ACK/NACK feedback mayoverlap.

In accordance with the present invention, the WTRU 102 and the Node-B104 utilizes new criteria for recognizing an RL failure. FIG. 4illustrates a scheme for recognizing an RL failure at the WTRU 102utilizing the HSUPA channels of the wireless communication system 100,as shown in FIG. 1. The WTRU 102 utilizes criteria based on reception onthe AGCH 108, the RGCH 110 and the HICH 112 according to specifiedprocedures known to the WTRU 102. The transceiver 202 of the WTRU 102sends a rate request 402 to the Node-B 104 for uplink transmission inaccordance with a rate request and scheduling procedure. In response,the scheduler 308 of the Node-B 104 sends scheduling assignments 406,(which is shown as a failed transmission in FIG. 4), back to the WTRU102 via an AGCH or a RGCH. The scheduling assignments 406 may or may notbe successfully received. If the WTRU 102 does not receive anyscheduling assignments 406 or HARQ feedback 404 after sending the raterequest 402, (preferably multiple times or over a specified period), theWTRU 102 recognizes that the rate request and scheduling procedure hasfailed and declares a radio link failure which invokes a procedure forrecovering the connection.

The measurement unit 206 of the WTRU 102 shown in FIG. 2 may alsomeasure channel quality on the AGCH 108 and the RGCH 110. If the channelquality on the AGCH 108 or the RGCH 110 falls below a predeterminedthreshold for a predetermined period of time, the WTRU 102 recognizesthat the rate request and scheduling procedure has failed and declaresan RL failure which invokes a procedure for recovering the RL. Thequality of the AGCH 108 and the RGCH 110 may be evaluated based onsignal-to-interference ratio (SIR), received energy per chip(E_(b))/power density in the band (N_(o)), block error rate (BLER) orany other relevant criteria.

If the WTRU 102 successfully receives a scheduling assignment 406, theWTRU 102 initiates a UL data transmission 408 in accordance with the ULscheduling assignment 406. In response to the UL data transmission 408,the Node-B 104 sends H-ARQ feedback 410 on the HICH 112, (which is shownas a failed transmission in FIG. 4), to the WTRU 102. If the WTRU 102fails to receive an ACK on the HICH 112, (preferably multiple times orover a specified period), the WTRU 102 recognizes that the UL datatransmission and H-ARQ procedure has failed and declares an RL failurewhich invokes a procedure for recovering the RL. If the ACK/NACK ratioof the UL data transmission falls below a predetermined threshold, theWTRU 102 may also recognize that the RL has failed.

The measurement unit 206 of the WTRU 102, as shown in FIG. 2, alsomonitors channel quality on the HICH 112. If the channel quality on theHICH 112 falls below a predetermined threshold for a predeterminedperiod of time, the WTRU 102 recognizes that the UL data transmissionand H-ARQ procedure has failed and declares an RL failure which invokesa procedure for recovering the RL. The quality of the HICH 112 may beevaluated based on SIR, E_(b)/N_(o), BLER or any other relevantcriteria.

If either of the AGCH 108 or the RGCH 110 reduces the SRB or other RBsutilizing HSUPA to a data rate below an acceptable threshold, the WTRUrecognizes that the RL has failed.

If the SRBs supported by HSUPA channels are not assigned a guaranteedbit rate, and therefore the WTRU 102 is required to send a rate request,and scheduling assignments are sent back in response to the raterequest, the reception on the AGCH 108 and the RGCH 110 is used todetermine RL failure. Otherwise, if the SRBs supported by HSUPA channelsare assigned a guaranteed bit rate, the reception criteria of the AGCH108 and the RGCH 110 for RL failure may not be applied.

Multiple RGCHs 110 and HICHs 112 may be configured for the WTRU 102 and,in each cell, the RGCH 110 and the HICH 112 may utilize a commonphysical channel. RL failure based on HICH transmissions can be declaredonly if the reception is not achieved on any of the HICH channels. Anexception may apply if an HICH transmission has failed on the primaryserving Node-B. RL failure based on the RGCH transmissions may bedeclared if any one RGCH 110 reduces the rate below the predeterminedthreshold.

Criteria for RL failure detection in the WTRU 102 is specified for UTRANconfiguration changes that result in disabling HSUPA transmission in theWTRU 102. When SRBs are utilizing HSUPA, UTRAN controlled configurationchanges which result in disabling HSUPA operation in the WTRU 102 areused as an additional RL failure detection criteria.

FIG. 5 illustrates a scheme for detecting RL failure at the Node-B 104utilizing the HSUPA channels of the wireless communication system 100,as shown in FIG. 1. The Node-B 104 utilizes criteria based on receptionon the E-DPDCH 106 and the E-DPCCH 114. The transceiver 202 of the WTRU102 sends a rate request 502, (which is shown as a failed transmissionin FIG. 5), to the Node-B 104 for enhanced uplink transmission. The WTRU102 sends rate requests 502 upon arrival of new HSUPA data to transmitand may also be configured to send a rate request 502 periodically. Theperiodicity configured for WTRU rate request reporting in advance ofand/or following an initial rate request resulting in the transmissionof scheduling information may be known to the Node-B 104. WTRU raterequests 502 may also be generated in response to a request from theNode-B 104. In response to a rate request 502, the Node-B sends H-ARQfeedback 504 to the WTRU 102 over the HICH 112, and also sends a ULscheduling assignment 506 to the WTRU 102 over the AGCH 108 or the RGCH110. Based on specified rate request procedures, the Node-B 104 may usethe knowledge of lost rate requests 502, (including a periodic requestor a polled request), as criteria for RL failure detection.

The measurement unit 306 of the Node-B 104, as shown in FIG. 3, alsomeasures channel quality of the E-DPCCH 114 from the WTRU 102. If thechannel quality of the E-DPCCH 114 remains below a predeterminedthreshold for a predetermined period of time, the Node-B 104 may alsodeclare RL failure. The Node-B 104 may also use knowledge of when theE-DPCCH 114 is known to be active based on knowledge of scheduled andnon-scheduled grants signaled to the WTRU 102. The quality of theE-DPCCH 114 may be evaluated based on SIR, E_(b)/N_(o), BLER or anyother relevant criteria.

As shown in FIG. 5, in response to receiving the UL schedulingassignment 506, the WTRU 102 sends a UL data transmission 508, (which isshown as a failed transmission in FIG. 5) to the Node-B 104. If theNode-B 104 receives no response following the transmission of the ULscheduling assignment 506, (preferably after several consecutivefailures or a statistical failure threshold is reached), the Node-B 104may declare RL failure. If the Node-B 104 has knowledge of synchronousH-ARQ retransmissions followed by H-ARQ feedback 504 including a NACK,or if the Node-B 104 receives an old data packet followed by H-ARQfeedback 504 including an ACK, (preferably after several consecutivefailures or a statistical failure threshold is reached), the Node-B 104may declare RL failure. The Node-B 104 may also use an ACK/NACK ratio onfinal data retransmissions from the WTRU 102 as criteria for RL failure.

Additionally or alternatively, the RL failure may be determined by aradio network controller (RNC). In this case the Node-B 104 providesnecessary information to the RNC, such as E-DPCCH quality, rate requestreception statistics, H-ARQ data transmission statistics, (i.e.,ACK/NACK information), and/or E-DPDCH and E-DPCCH BLER.

If improper operation of at least one of the E-DPCCH 114 and the E-DPDCHoccurs, a failure of data transmission 508 from the WTRU 102 isdetected, and the Node-B 104 recognizes that the RL has failed andinvokes a procedure for releasing the RL. If the Node-B 104 successfullyreceives the UL data transmission 508, the Node-B 104 sends H-ARQfeedback 510 to the WTRU 102 on the HICH 112

FIG. 6 shows HSDPA channels established between the WTRU 102 and theNode-B 104. In HSDPA, scheduling assignments for downlink (DL)transmissions is transmitted on a high speed shared control channel(HS-SCCH) 602 from the Node-B 104 to the WTRU 102. Using schedulinginformation received on the HS-SCCH 602, the WTRU 102 receives the datatransmission on a high speed physical downlink shared channel (HS-PDSCH)604. The WTRU 102 then transmits H-ARQ feedback, (i.e., ACK or NACK),and a channel quality indication (CQI) to the Node-B 104 via a highspeed dedicated physical control channel (HS-DPCCH) 606. Thistransmission procedure applies to each operational HARQ process in theWTRU 102.

In accordance with the present invention, the WTRU 102 utilizes criteriafor recognizing an RL failure based on reception on the HS-SCCH 602 andthe HS-PDSCH 604. FIG. 7 illustrates a scheme for recognizing an RLfailure at the WTRU 102 utilizing HSDPA in accordance with the presentinvention. The scheduler 308 of the Node-B 104 sends DL schedulingassignment 702, (which is shown as a failed transmission in FIG. 7), tothe WTRU 102 via the HS-SCCH 602

The measurement unit 206 of the WTRU 102, as shown in FIG. 2, may alsomeasure channel quality on the HS-SCCH 602. If the channel quality ofthe HS-SCCH 602 remains below a predetermined threshold over apredetermined period of time, the WTRU 102 declares an RL failure. Useof this criteria is based on WTRU knowledge of HS-SCCH activity.

Referring to FIG. 7, if the WTRU 102 successfully receives the DLscheduling assignment 702 on the HS-SCCH 602, the WTRU 102 attempts toreceive data transmission 704, (which is shown as a failed transmissionin FIG. 7), via the HS-PDSCH 604 in accordance with the received DLscheduling assignment 702. The measurement unit 206 of the WTRU 102monitors channel quality of the HS-PDSCH 604 and, if the channel qualityof the HS-PDSCH 604 remains below a predetermined threshold over apredetermined period of time, the WTRU 102 may declare an RL failure andinvoke a procedure for recovering the RL. The channel quality of theHS-SCCH 602 and the HS-PDSCH 604 may be evaluated based on SIR,E_(b)/N_(o), BLER or any other relevant criteria. If the WTRU 102successfully receives the data transmission 704, the WTRU 102 sends anH-ARQ feedback 706 including an ACK on the HS-DPCCH 606.

The controller 204 of the WTRU 102, as shown in FIG. 2, may furthermonitor an ACK/NACK ratio from CRC on the HS-PDSCH transmissions. If theACK/NACK ratio is below a specified threshold, the WTRU 102 may declarean RL failure. The measurement unit 206 and the controller 204 of theWTRU 102 may further generate and send a CQI, preferably based on commonpilot channel (CPICH) reception. If the measured channel quality isbelow a configured threshold (preferably over a specified time period),the WTRU 102 may declare an RL failure.

Criteria for the RL failure detection in the WTRU 102 should bespecified for UTRAN configuration changes that result in disabling HSDPAreception in the WTRU 102. When SRBs are utilizing HSDPA, UTRANcontrolled configuration changes which result in disabling HSDPAoperation in the WTRU 102 are used as an additional RL failure detectioncriteria.

In accordance with the present invention, the Node-B 104 utilizescriteria for recognizing an RL failure based on reception on theHS-DPCCH 606. FIG. 8 illustrates a scheme for recognizing an RL failureat the Node-B 104 utilizing HSDPA in accordance with the presentinvention. The WTRU 102 sends an H-ARQ feedback 806, (which is shown asa failed transmission in FIG. 8), after receiving a channel allocation802 and data transmission 804 from the Node-B 104. The WTRU 102 mayadditionally be configured for periodic CQI reporting to Node-B 104.Node-B knowledge of the H-ARQ feedback and CQI reporting, by specifiedsignaling procedures, allows Node-B detection of HS-DPCCH failures. Themeasurement unit 306 of the Node-B 104, as shown in FIG. 3, may alsomonitor channel quality of the HS-DPCCH 606, and if the channel qualityof the HS-DPCCH 606 remains below a predetermined threshold over aspecified time period, the controller 304 of the Node-B 104 declares anRL failure. The quality of the HS-DPCCH 606 may be evaluated based onSIR, E_(b)/N_(o), BLER or any other relevant criteria.

The controller 304 of the Node-B 104 may further use the reported CQI oran ACK/NACK ratio as criteria for the RL failure detection. If anaverage of the reported CQI or an ACK/NACK ratio over a sliding windowperiod is below a threshold, or if an average of the number of discardedMAC-hs transmissions is above a threshold, the controller 304 of theNode-B 104 may declare an RL failure.

The RL failure may be determined by an RNC. In this case, the Node-B 104reports necessary information to the RNC such as HS-DPCCH qualitystatistics, reported CQI, H-ARQ ACK/NACK indications, or MAC-hstransmission failure indications.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

What is claimed is:
 1. A user equipment (UE) comprising: a measurementunit to monitor a high speed downlink packet access (HSDPA) channel,wherein the HSDPA channel includes at least one of a high speed sharedcontrol channel (HS-SCCH), and a high speed physical downlink sharedchannel (HS-PDSCH), and to determine a channel quality of the HSDPAchannel, wherein the channel quality is determined based at least inpart on a signal-to-interference ratio (SIR), received energy per chip(E_(b))/power density (N_(o)), or a block error ratio (BLER); and acontroller coupled with the measurement unit, the controller to declarea radio link failure if a channel quality of the HSDPA channel remainsbelow a predetermined threshold over a predetermined period of time, andto invoke a procedure to recover the radio link.
 2. A user equipment asclaimed in claim 1, further comprising a transceiver to transmit hybridautomatic repeat request (H-ARQ) feedback on the HS-DPCCH in response toreceiving a successful transmission on the HS-SCCH or the HS-PDSCH.
 3. Auser equipment as claimed in claim 1, wherein a radio link failurefurther may be declared if an acknowledgement (ACK) to negativeacknowledgment (NACK) ratio falls below a predetermined threshold.
 4. Auser equipment as claimed in claim 1, wherein the channel quality isdetermined based at least in part on a common pilot channel (CPICH)reception.
 5. A user equipment as claimed in claim 1, further comprisinga transceiver to transmit a channel quality indicator (CQI) in responseto the determined channel quality.
 6. A wireless transmit/receive unit(WTRU), comprising: a measurement unit to determine a channel quality ofa physical shared control channel, wherein the channel quality isdetermined based at least in part on a signal-to-interference ratio(SIR), received energy per chip (E_(b))/power density (N_(o)), or ablock error ratio (BLER); and a controller coupled with the measurementunit, the controller to determine a radio link failure if the channelquality of the physical shared control channel remains below apredetermined threshold over a predetermined period of time, and toinvoke a procedure to recover the radio link.
 7. A wirelesstransmit/receive unit (WTRU) as claimed in claim 6, further comprising atransceiver to transmit hybrid automatic repeat request (H-ARQ) feedbackin response to receiving a transmission.
 8. A wireless transmit/receiveunit (WTRU) as claimed in claim 6, wherein a radio link failure furthermay be determined if an acknowledgement (ACK) to negative acknowledgment(NACK) ratio falls below a predetermined threshold.
 9. A wirelesstransmit/receive unit (WTRU) as claimed in claim 6, wherein the channelquality is determined based at least in part on a common pilot channel(CPICH) reception.
 10. A wireless transmit/receive unit (WTRU) asclaimed in claim 6, further comprising a transceiver to transmit achannel quality indicator (CQI) in response to the determined channelquality.